Hydrofluoroolefins (HFOs), as compared with chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), do not contain chlorine and do not pose a threat to the Earth's ozone layer, meanwhile have a low Global Warming Potential, which have now become the focus of research in F-chemical industries. 2,3,3,3-tetrafluoropropene, i.e., HFO-1234yf, as one of hydrofluoroolefins, has an ozone depletion potential of 0, has a Global Warming Potential of 4, and can be widely used as refrigerants, extinguishing agents, heat-transfer media, propellants, foaming agents, blowing agents, gaseous media, sterilizing agent carriers, monomer of polymers, granular-removing fluids, carrier gas fluids, abrasive polishing agents, alternative desiccants and electrical cycle working fluids.
WO2009153493 discloses a process for the preparation of HFO-1234yf with 1,1,1,2,2,3-hexafluoropropane (HFC-236cb) as a raw material, in which HFC-236cb firstly undergoes dehydrofluorination in the presence of hydrogen and the catalyst Ni—Cr/AlF3 to generate 1,2,3,3,3-pentafluoropropylene (HFC-1225ye), then HFC-1225ye undergoes hydrogenation to obtain 1,1,1,2,3-pentafluoropropane (HFC-245eb), and finally undergoes dehydrofluorination reaction in the presence of hydrogen to obtain HFO-1234yf.
US20110190554 discloses a process for the synthesis of HFO-1234yf with 1,1,2,3,3,3-hexafluoropropene (HFP) as a raw material by four steps of reactions including hydrogenation, dehydrofluorination, hydrogenation and dehydrofluorination.
In the above-mentioned two synthetic methods, the reaction materials are difficult to obtain, many reaction steps are required, the cost is high, and at least the stoichiometric amount of hydrogen is need to be introduced. The hydrogenation step usually uses a higher molar ratio in order to effectively control the exothermicity of the reaction. In addition, introduction of excessive hydrogen at a relatively high temperature will increase relevant safety risks, and the conditions are harsh, which are not conducive to industrial production.
US2011207975 discloses a process for the synthesis of HFO-1234yf with 1,1,2,3-tetrachloropropene (TCP) or 1,1,1,2,3-pentachloropropane (HCC-240db) as a raw material. In the method, firstly TCP or HCC-240db undergoes gas-phase fluorination with HF in the presence of Cr2O3 catalyst in a first reactor to obtain 2-chloro-3,3,3-trifluoropropene (HCFC-1233xf), and then HCFC-1233xf undergoes liquid-phase fluorination in a second reactor under the action of SbCl5 to obtain 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), and finally HCFC-244bb undergoes dehydrochlorination reaction in a third reactor to obtain HFO-1234yf.
WO2012099776 discloses a process for the preparation of HFO-1234yf from TCP by integrated three steps via HCFC-1233xf and HCFC-244bb.
WO2009125199 discloses a process for the preparation of HFO-1234yf from 2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) via HCFC-1233xf and HCFC-244bb.
For the above-mentioned preparation methods, firstly, they relate to chromium-based catalysts such as Cr2O3 and Cr2O3 supported on alumina or fluorinated alumina. In fact, the catalysts used in industrial production and application of HFCs are also chromium-based catalysts. These chromium-containing compounds and catalysts will cause damage to human digestive tract and kidney, especially high-valence chromium has a strong carcinogenic effect, and they are unfriendly to human and the environment in the process of production and use, and will cause serious harm. Secondly, the above methods all relate to the intermediates HCFC-1233xf and HCFC-244bb. These two halogenated hydrocarbons have approximate boiling points and azeotrope-like properties, and both of them are also easy to form an azeotrope with HF. Hence, a problem of difficult separation occurs, and the mixtures of them cannot be separated effectively by standard process and conventional methods, especially when they form a binary azeotrope or azeotrope-like component. Additionally, it has been found that during the preparation of HFO-1234yf from HCFC-244bb by dehydrochlorination, the HCFO-1233xf and HF impurities contained therein can seriously affect the life and product selectivity of the dehydrochlorination catalyst, and easily lead to a decrease in HFO-1234yf selectivity and in activity of the catalyst and loss of the catalyst life.
Although many methods have been currently disclosed for preparing HFO-1234yf, they have the deficiencies such as the harsh reaction conditions, unfriendliness of the catalyst to environment, difficulty in separating the reaction intermediates, energy consumption and cost increase due to too many reaction steps, and low selectivity of the target product. Thus, there is a need for continuous improvement and more effective preparation methods.